Cooperative mimo in multicell wireless networks

ABSTRACT

A method and system for cooperative multiple-input multiple output (MIMO) transmission operations in a multicell wireless network. Under the method, antenna elements from two or more base stations are used to form an augmented MIMO antenna array that is used to transmit and received MIMO transmissions to and from one or more terminals. The cooperative MIMO transmission scheme supports higher dimension space-time-frequency processing for increased capacity and system performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 12/130,277 entitled COOPERATIVE MIMO IN MULTICELLWIRELESS NETWORKS, filed on May 30, 2008; which is acontinuation-in-part of and claims priority to U.S. patent applicationSer. No. 11/007,570, now U.S. Pat. No. 7,428,268, filed on Dec. 7, 2004;all of the disclosures of which are expressly incorporated by referenceherein.

TECHNICAL FIELD

The present invention relates to the field of communications systems;more particularly, the present invention relates to techniques forperforming MIMO operations in a multicell wireless network.

BACKGROUND OF THE INVENTION

With high-speed wireless services increasingly in demand, there is aneed for more throughput per bandwidth to accommodate more subscriberswith higher data rates while retaining a guaranteed quality of service(QoS). In point-to-point communications, the achievable data ratebetween a transmitter and a receiver is constrained by the availablebandwidth, propagation channel conditions, as well as thenoise-plus-interference levels at the receiver. For wireless networkswhere a base-station communicates with multiple subscribers, the networkcapacity also depends on the way the spectral resource is partitionedand the channel conditions and noise-plus-interference levels of allsubscribers. In current state-of-the-art, multiple-access protocols,e.g., time-division multiple access (TDMA), frequency-divisionmultiple-access (FDMA), code-division multiple-access (CDMA), are usedto distribute the available spectrum among subscribers according tosubscribers' data rate requirements. Other critical limiting factors,such as the channel fading conditions, interference levels, and QoSrequirements, are ignored in general.

The fundamental phenomenon that makes reliable wireless transmissiondifficult to achieve is time-varying multipath fading. Increasing thequality or reducing the effective error rate in a multipath fadingchannel may be extremely difficult. For instance, consider the followingcomparison between a typical noise source in a non-multipath environmentand multipath fading. In environments having additive white Gaussiannoise (AWGN), it may require only 1- or 2-db higher signal-to-noiseratio (SNR) using typical modulation and coding schemes to reduce theeffective bit error rate (BER) 10⁻² from 10⁻³. Achieving the samereduction in a multipath fading environment, however, may require up to10 db improvement in SNR. The necessary improvement in SRN may not beachieved by simply providing higher transmit power or additionalbandwidth, as this is contrary to the requirements of next generationbroadband wireless systems.

One set of techniques for reducing the effect of multipath fading is toemploy a signal diversity scheme, wherein a combined signal is receivedvia independently fading channels. Under a space diversity scheme,multiple antennas are used to receive and/or send the signal. Theantenna spacing must be such that the fading at each antenna isindependent (coherence distance). Under a frequency diversity scheme,the signal is transmitted in several frequency bands (coherence BW).Under a time diversity scheme, the signal is transmitted in differenttime slots (coherence time). Channel coding plus interleaving is used toprovide time diversity. Under a polarization diversity scheme, twoantennas with different polarization are employed for reception and/ordivision.

Spatial diversity is commonly employed in modern wireless communicationssystems. To achieve spatial diversity, spatial processing with antennaarrays at the receiver and/or transmitter is performed. Among manyschemes developed to date, multiple-input multiple-output (MIMO) andbeamforming are the two most studied and have been proved to beeffective in increase the capacity and performance of a wirelessnetwork, (see, e.g., Ayman F. Naguib, Vahid Tarokh, Nambirajan Seshadri,A. Robert Calderbank, “A Space-Time Coding Modem for High-Data-RateWireless Communications”, IEEE Journal on Selected Areas inCommunications, vol. 16, no. 8, October 1998 pp. 1459-1478). In a blocktime-invariant environment, it can be shown that in a system equippedwith Nt transmit antennas and Nr receive antennas, a well designedspace-time coded (STC) systems can achieve a maximum diversity of Nr*Nt.Typical examples of STC include space-time trellis codes (STTC) (see,e.g., V. Tarokh, N. Seshadri, and A. R. Calderbank, “Space-time codesfor high data rate wireless communication: performance criterion andcode construction”, IEEE Trans. Inform. Theory, 44:744-765, March 1998)and space-time block codes from orthogonal design (STBC-OD) (see, e.g.,V. Tarokh, H. Jafarkhani, and A. R. Calderbank, “Space-time block codesfrom orthogonal designs”, IEEE Trans. Inform. Theory, 45:1456-1467, July1999.)

Since the capacity and performance of an MIMO system depends criticallyon its dimension (i.e., Nt and Nr) and the correlation between antennaelements, larger size and more scattered antenna arrays are desirable.On the other hand, costs and physical constraints prohibit the use ofexcessive antenna arrays in practice.

BRIEF SUMMARY OF THE INVENTION

A method and system is disclosed herein for cooperative multiple-inputmultiple output (MIMO) transmission operations in a multicell wirelessnetwork. Under one embodiment, antenna elements from two or more basestations are used to form an augmented MIMO antenna array that is usedto transmit and receive MIMO transmissions to and from one or moreterminals.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features which are believed to be characteristic ofthe invention, both as to its organization and method of operation,together with further objects and advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawing, in which:

FIG. 1 depicts a multicell scenario where antenna elements from multiplebase-stations are augmented to form a higher dimension MIMO transceiverarray;

FIG. 2 shows a generic channel matrix H used for modeling the capacityof MIMO systems;

FIG. 3 shows the capacity increase of an MIMO system with respect to thenumber of transmitting antennas;

FIG. 4 a shows a cooperative MIMO architecture under which antennaarrays from two base stations are employed in a cooperative MIMOtransmission scheme to transmit downlink signals to one terminal;

FIG. 4 b shows aspects of the cooperative MIMO architecture of FIG. 4 aemployed for transmitting and processing uplink signals received by theaugmented antenna array;

FIG. 5 shows an extension to the cooperative MIMO architecture of FIG. 4a, wherein beamforming is used to direct a MIMO transmission toward oneterminal while performing spatial nulling towards another terminal;

FIG. 6 shows a cooperative MIMO architecture under which two basestations performing multiuser MIMO with two terminals simultaneouslyusing joint encoding and decoding;

FIG. 7 a shows a block diagram of an MIMO OFDM encoder/transmitter;

FIG. 7 b shows the block diagram of an MIMO OFDM encoder/transmitterwith beamforming;

FIG. 8 shows a block diagram of an MIMO OFDM receiver/decoder;

FIG. 9 shows a block diagram used to model a space-time codingtransmission;

FIG. 10 shows an exemplary PSK-based space-time trellis code (SITC)encoder;

FIG. 11 shows an exemplary QAM-based STTC encoder;

FIG. 12 shows a block diagram used to model a space-time block coding(STBC) transmission scheme;

FIG. 13 a shows a block diagram modeling an STTC delay diversity scheme;

FIG. 13 b shows a block diagram modeling an STBC delay diversity scheme;

FIG. 14 is a block diagram of an exemplary PSK-based SITC delaydiversity encoder;

FIG. 15 is a schematic diagram illustrating a cooperative MIMOarchitecture under which STC encoding operations are performed at amaster encoder;

FIG. 16 is a schematic diagram illustrating a cooperative MIMOarchitecture under which STC encoding operations are performed onrespective instances of replicated data streams at multiple basestations;

FIG. 17 a shows a cooperative MIMO architecture under which antennaarrays from multiple terminals are employed in a cooperative MIMOtransmission scheme to transmit uplink signals to one or more basestations;

FIG. 17 b shows aspects of the cooperative MIMO architecture of FIG. 17a employed for transmitting and processing downlink signals received bythe augmented antenna array;

FIG. 18 shows a cooperative MIMO architecture under which multipleterminals perform multiuser MIMO with multiple base stationssimultaneously using joint encoding and decoding;

FIG. 19 a shows a block diagram of another MIMO OFDMencoder/transmitter;

FIG. 19 b shows the block diagram of another MIMO OFDMencoder/transmitter with beamforming; and

FIG. 20 shows a block diagram of another MIMO OFDM receiver/decoder.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with aspects of the present invention, a method andapparatus to augment antenna elements from two or more base-stationsand/or terminals to perform higher dimensional MIMO operations isdisclosed. In one implementation, MIMO/joint space-time coding isemployed across multiple base stations in a cellular environment,wherein the cooperative transmission of signals is performed at themodulation and coding level. According to another embodiment, MIMO/jointspace-time coding is employed across multiple terminals in a similarfashion. This novel approach introduces additional diversities andcapacities to existing network components with minimal additional costs.Because of the increase in the number of transmit antennas, the numberof simultaneous users increases, leading to better spectrum efficiency.

In the following description, numerous details are set forth to providea more thorough explanation of the present invention. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without these specific details. In other instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention.

Some portions of the detailed descriptions which follow are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take thefoiin of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CDROMs, and magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, and each coupled to a computer systembus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; electrical, optical,acoustical or other form of propagated signals (e.g., carrier waves,infrared signals, digital signals, etc.); etc.

Overview

FIG. 1 depicts three cells 100, 102, and 104 for a typical wirelessnetwork with multiple base stations BS1, BS2 and BS3 and terminals A, B,and C. Each of base stations BS1 and BS2 includes a 4-element circularantenna array, while terminal A has two antennas 1 and 2.

From a theoretical viewpoint, the capacity between a transmitter and areceiver for a MIMO transmission scheme is determined by the vectorchannel H, which is also referred to as the channel matrix. Asillustrated in FIG. 2, the channel matrix H includes M rows and Ncolumns, wherein M is the number of receiver antennas (Rx) and N is thenumber of transmitter antennas (Tx). In the illustrated channel matrixH, each entry α_(ij) is the complex channel gain from the i-th transmitantenna to the j-th receive antenna.

The channel capacity for a Single-Input Single-Output (SISO) channel is,

C=log₂(1+p) bits/sec/use  (1),

where p is the signal to noise ratio. The channel capacity for a MIMOchannel is,

$\begin{matrix}{C = {\log_{2}{{\det \left\lbrack {I + {\frac{P}{N}{HH}^{*}}} \right\rbrack}.}}} & (2)\end{matrix}$

From the above, the outage capacity can be shown to be,

$\begin{matrix}{C = {\frac{1}{2}M\; {{\log_{2}\left( {1 + {\sigma \left\{ h \right\}^{2}p}} \right)}.}}} & (3)\end{matrix}$

It is observed that under equation (3), the capacity increases linearlywith the number of receive antennas when M is large. The channelcapacity limit grows logarithmically when adding an antenna array at thereceiver side (Single-Input Multiple-Output—SIMO). Meanwhile, thechannel capacity limit grows as much as linearly with min(M, N), whichis the maximum number of spatial eigenmodes, in the case of a MIMOsystem. An illustration of a MIMO system capacity as a function ofchannel matrix dimension is shown in FIG. 3.

Since the system capacity is dictated by the dimension (number ofantennas) and the condition (correlation between antenna elements) ofthe channel, it is desirable to have large size antenna array with morescattered elements. However, there is a point of diminishing return,wherein the costs of adding antenna elements and correspondingprocessing complexity for a given base station or terminal exceeds thebenefit of the incremental increase in system capacity. Furthermore, toobtain the added benefit of extra capacity, it may be necessary to addadditional antenna elements to many or all base stations or terminalswithin a given wireless network.

Embodiments of the present invention take advantage of the benefit ofhaving large size antenna arrays with more scattered elements withoutrequiring additional antenna elements. This is accomplished byaugmenting the operations of antenna elements from two or moretransmitters to form a larger size antenna array. The augmented arrayperforms “cooperative MIMO” transmission operations for one or morereceivers. For example, FIG. 1 shows an exemplary use of a cooperativeMIMO transmission scheme, wherein the antenna elements for base stationsBS1 and BS2 are augmented to cooperatively communicate via receiveantennas 1 and 2 for terminal A.

FIG. 4 a depicts a block diagram of one embodiment of a downlink (frombase stations to terminals) cooperative MIMO architecture 400. Forillustrative purposes, the architecture shown in FIG. 4 a include twobase stations 402 and 404 and a single terminal 406. It will beunderstood that an actual implementation of MIMO architecture 400 mayinclude two or more base stations that transmit signals that arereceived by one or more terminals.

In the illustrated embodiment of FIG. 4 a, base station 402 has anantenna array including Nt₁ transmit antennas, while base station 404has an antenna array including Nt₂ antennas and terminal 406 includes Nrantennas. In view of the foregoing MIMO definitions, the cooperative useof the base station antennas increases the MIMO dimension to(Nt₁+Nt₂)*Nr. This increase in dimension is accomplished withoutrequiring any additional antenna elements at the base stations, as wellas the components use to drive the antennas.

According to aspects of various embodiments of the invention describedherein, an information bit sequence corresponding to data to betransmitted to a subscriber (e.g. terminal 406) may be space-time,space-frequency, or space-time-frequency coded, as depicted by a block408 in FIG. 4 a. In some embodiments, space-time, space-frequency, orspace-time-frequency codes may be augmented to support delay diversity,as described below. After appropriate encoding is performed in block408, the coded data is then passed to the base stations, whereupon it istransmitted via applicable antenna elements at those base stations. Thetwo or more base stations then perform joint MIMO transmissions(depicted as signals 410 and 412) towards the subscriber (e.g. a useroperating terminal 406) in view of applicable MIMO channel configurationparameters. For example, signals 410 and 412 transmitted from basestations 402 and 404 may employ selected antenna elements for each ofthe base stations based on the coding scheme and/or MIMO scheme that iscurrently employed for a particular subscriber. In general, cooperativeMIMO transmissions can be performed during regular communication, orduring handoff, where a subscriber moves across the boundary betweencells.

In one embodiment, space-time coding is employed. For example, incominginformation bits are space-time coded (using e.g., space-time block ortrellis codes) at block 408, and the encoded data are forwarded to eachof base stations 402 and 404. Further details of space-time blockencoding and the use of space-time trellis codes are discussed below.

In one embodiment, the space-time (or space-frequency, orspace-time-frequency) coding is performed at a master encoder. Inanother embodiment, the space-time (or space-frequency, orspace-time-frequency) is performed at separate locations (e.g., withinthe base stations) based on a common (replicated) information bitsequence received at each of the separate locations.

FIG. 4 b shows uplink signal processing aspects of cooperative MIMOarchitecture 400. In this instance, an uplink signal 414 is transmittedfrom terminal 406 via selected antennas from among transmit antennas1-Nt. The uplink signal 414 is received by the respective receiveantenna arrays (1-Nr₁, 1-Nr₂) for base stations 402 and 404. (It isnoted that the same antennas may be used for both transmit and receiveoperations for some embodiments, while separate sets of transmit andreceive antennas may be employed for other embodiments.) Upon beingreceived at the base stations, initial signal processing is performed onthe uplink signals, and the processed signals are forwarded to a block416 to perform joint MIMO decoding and demodulation, thus extracting theinformation bits corresponding to the data transmitted by terminal 406.In general, the components for performing the operations of block 416may be implemented in a master decoder that is centrally located withrespect to multiple base stations (e.g., base stations 402 and 404), ormay be located at one of the multiple base stations.

FIG. 5 depicts a multi-user cooperative MIMO architecture 500. Underthis embodiment, the augmented antenna array (comprising selectedtransmit antenna elements for base stations 502 and 504) is used toperform MIMO operation towards one or more intended subscribers whilelimiting the radio signal at the location/direction of un-intendedsubscribers using a beamforming and nulling scheme. For example,techniques are known for steering transmitted signals toward selectedlocations, while transmitted signals sent toward other directions arenullified due to signal canceling effects and/or fading effects.Collectively, these selective transmission techniques are referred to asbeamforming, and are accomplished by using appropriate antenna elements(an augmented array of antennas hosted by two or more base stationsunder the embodiments herein) and applicable control of the signalstransmitted from those antenna elements (e.g., via weighted inputsderived from feedback returned from a targeted terminal). Underbeamforming embodiments of the invention, current techniques employedfor antenna arrays located at a single base stations (see, e.g., D. J.Love, R. W. Heath Jr., and T. Strohmer, “Grassmannian Beam forming forMultiple-Input Multiple-Output Wireless Systems,” IEEE Transactions onInformation Theory, vol. 49, pp. 2735-2747, October 2003) are extendedto support beamforming operations via selected antenna elements hostedby multiple base stations. As described below, it may be necessary toemploy signal synchronization between multiple base stations to obtainthe desired beamforming results.

In the embodiment of FIG. 5, information bits are encoded using one ofspace-time, space-frequency, or space-time-frequency coding schemes in ablock 514. Block 514 is also employed to perform beamforming operations,as describe below in further detail with reference to FIG. 7 b. Theencoded output of block 514 is then provided to each of base stations502 and 504, which in turn transmit respective signals 516 and 518. Asdepicted by lobes 520, 522, and 524, the channel characteristics of thecombined signals 516 and 518 produce areas of higher gain in certaindirections. At the same time, the gain of the combined signals 516 and518 in other directions, such as depicted by a null direction 526, maybe greatly reduced (e.g., to the point at which the signal cannot bedecoded) due to spatial nulling. In one embodiment, spatial nulling isperformed at the direction of un-intended subscribers.

For example, under the scenario illustrated in FIG. 5, the combinedsignals 516 and 518 are controlled so as to produce a high gain withinlobe 522. As such, terminal 506 receives a good signal at its antennaarray, and can decode the combined MIMO signal using appropriate MIMOdecoding techniques that are well-known in the wireless communicationsystem arts. Meanwhile, the strength of the combined signal received ata terminal 528 is nulled using spatial nulling. Accordingly, datacorresponding to the information bits received at block 514 istransmitted to only terminal 506, and is not received by terminal 528.

FIG. 6 depicts another multi-user cooperative MIMO architecture 600.Instead of forming nulls to un-intended terminals, information frommultiple users is jointed encoded, transmitted from multiple basestations via the augmented MIMO antenna array, and then decoded at thereceiving terminals. In one embodiment of the invention, the informationis decoded at the user ends independently. The signals intended forother users are treated as interference. In another embodiment, theinformation from all users are decoded jointly. In yet anotherembodiment, the information received at different user locations areconsolidated for joint decoding.

The embodiment of FIG. 6 shows an example of joint decoding. In thisinstance, information to be sent to terminals 1 (606) and 2 (628) isjointly encoded using one of space-time, space-frequency, orspace-time-frequency coding in a block 630. For clarity, the respectiveinformation to be sent to terminals 1 and 2 is depicted as data A anddata B. The jointly encoded output of block 630 is provided as inputs toeach of base stations 602 and 604. The base stations then transmit thejointly encoded data via selected antennas (corresponding to MIMOchannels assigned to terminals 1 and 2) to terminals 606 and 628. Uponreceipt of the jointly encoded data, it is decoded via operationsperformed in a block 632 for each of terminals 606 and 628. Upon beingdecoded, information intended for each recipient terminal is kept, whileother information is discarded. Accordingly, terminal 606 keeps data Aand discards data B, while terminal 628 keeps data B and discards dataA. In one embodiment, information to keep and discard is identified bypacket headers corresponding to packets that are extracted from thedecoded data received at a given terminal.

A block diagram corresponding to one embodiment of an OFDMA (OrthogonalFrequency Division Multiple Access) encoding/transmitter module 700A fora base station having N_(t) transmit antennas is shown in FIG. 7 a.Information bits for each of 1-N subcarriers are received at respectivespace-time coding (STC) blocks 704 _(1-N). The size of the STCs is afunction of the number of transmit antennas Nt. In general, thespace-time codes may comprise space-time trellis codes (STTC),space-time block codes (STBC), as well as STTC or STBC with delaydiversity, details of which are described below. Based on the applicableSTC, each of blocks 704 _(1-p) outputs a set of code words c₁[j,k] toc_(Nt)[j,k], wherein j represents the sub-channel index and k is thetime index. Each of the code words is then forwarded to an appropriateFast Fourier Transform (FFT) blocks 706 _(1-Nt). The outputs of the FFTblocks 706 _(1-Nt) are then fed to parallel to serial (P/S) conversionblocks 708 _(1-Nt), and cyclic prefixes are added via add cyclic prefix(CP) blocks 710 _(1-Nt). The outputs of add CP blocks 710 _(1-Nt) arethen provided to transmit antennas 1-Nt to be transmitted as downlinksignals to various terminals within the base station's coverage area.

A block diagram corresponding to one embodiment of an OFDMAreceiver/decoder module 800 for a terminal having N_(r) receive antennasis shown in FIG. 8. The signal processing at the receive end of adownlink signal is substantially the inverse of the process used forencoding and preparing the signal for transmission. First, the cyclicprefix for each of the signals received at respective receive antennas1-Nr is removed by a respective remove CP block blocks 810 _(1-Nr). Therespective signals are then fed into respective serial-to-parallel (S/P)conversion blocks 808 _(1-Nt) to produce parallel sets of data, whichare then provided as inputs to FFT blocks 806 _(1-Nr). The outputs ofFFT blocks 806 _(1-Nr) are then forwarded to appropriate STC decodingblocks 804 _(1-N) for decoding. The decoded data is then output at theinformation bits for subcarriers 1-N.

A block diagram corresponding to one embodiment of an OFDMAencoding/beamforming/transmitter module 700B that performs beamformingis shown in FIG. 7 b. As depicted by like-numbered blocks, much of thesignal processing performed by the embodiments of FIGS. 7 a and 7 b issimilar. In addition to these processing operations, OFDMAencoding/beamforming/transmitter module 700B further includesbeamforming blocks 705 _(1-N). Each of these beamforming blocks appliesa weighted value W_(1-N) to its respective inputs in view of controlinformation provided by a beamforming control block 712, which isgenerated in response to beamforming feedback data 714. Furtherdifferences between the embodiments of FIGS. 7 a and 7 b include STCblocks 704A_(1-N), which now employ STCs having a size L, whichrepresents the number of beamforming channels.

It should be appreciated that the cooperative MIMO concepts describedherein, both in the downlink and the uplink, also apply at the terminalside of a network. Virtual antenna arrays at the terminals, comprisingone or more antenna elements from a plurality of terminals, enablecooperative downlink reception and cooperative uplink transmission.FIGS. 17 a and 17 b show components of a wireless network according tovarious embodiments of the inventions described herein that enableterminal side cooperative MIMO applications.

FIG. 17 b shows downlink signal processing aspects of cooperative MIMOarchitecture 1700. As shown, network 1700 comprises a plurality ofterminals, e.g., terminals 1706, 1708, and 1710, each having antennaarrays where terminal 1706 has Nt₁ transmit antennas and Nr₁ receiveantennas, terminal 1708 has Nt₂ transmit antennas and Nr₂ receiveantennas, and terminal 1710 has Nt₃ transmit antennas and Nr₃ receiveantennas. Base station 1702 has an antenna array including Nt₁ transmitantennas and Nr₁ receive antennas and base station 1704 has an antennaarray including Nt₂ transmit antennas and Nr₂ receive antennas. In viewof the foregoing MIMO definitions, the cooperative use of the basestation antennas increases the MIMO dimension to(Nt₁+Nt₂+Nt₃)*(Nr₁+Nr₂+Nr₃).

According to a preferred embodiment, cooperative MIMO downlink receptionis achieved by exchanging data between a plurality of terminals, e.g.,terminals 1706, 1708, and 1710. Data exchange between terminals isexecuted via a short distance, high throughput radio link 1712.According to a preferred embodiment, short distance radio link 1712 is alink according to the IEEE 802.15 standard (e.g., Bluetooth), wirelessUSB, and the like. According to other embodiments, data may be exchangedbetween terminals using in-band radio communications, where, forexample, one or more terminals functions as a relay.

Downlink signals, e.g., downlink signal 1714, are transmitted from basestations 1702 and/or base station 1704 via selected transmit antennasamong available transmit antennas at each of base station 1702 and basestation 1704, i.e., 1-Nt₁ transmit antennas at base station 1702 and1-Nt₂ transmit antennas at 1704. Downlink signal 1714 is received by thereceive antenna arrays (1-Nr₁, 1-Nr₂, 1-Nr₃) for terminals 1706, 1708,and 1710, respectively. As discussed above, it should be appreciatedthat the same antennas may be used for both transmit and receiveoperations for some embodiments, while separate sets of transmit andreceive antennas may be employed for other embodiments.

Upon being received at the terminals, initial signal processing isperformed on the downlink signals at terminals 1706, 1708, and 1710, andthe processed signals are forwarded to a block 1716 to perform jointMIMO decoding and demodulation, thus extracting the information bitscorresponding to the data transmitted by base stations 1702 and/or 1704.According to a preferred embodiment, the components for performing theoperations of block 1716 are located at each terminal; that is, decoder1716 is co-located at each terminal. In such case decoder 1716 decodesonly bit streams targeted for the specific terminal at which it islocated. This is accomplished using signals from its own antennas aswell as antenna signals exchanged from other terminals. In anotherembodiment, the components for performing the operations of block 1716may be implemented in a master decoder that is centrally located withrespect to multiple terminals (e.g., 1706, 1708, and 1710), or may beco-located at one of the terminals.

According to another embodiment of the invention described herein, oneor more terminals receives downlink signals, determines whether thedownlink signals comprise cooperative MIMO signals or signals from asingle base station, and decodes the received signals according to thatdetermination. In such case, decoding may be performed at the receivingterminal or performed at centralized location, e.g., a centralizedmaster decoder.

FIG. 17 a depicts a block diagram of one embodiment of an uplinkcooperative MIMO architecture 1700. Similar to downlink conceptsdiscussed herein, cooperative MIMO uplink concepts are particularlyuseful in cases where there is a weak signal path between a base stationand a first terminal. In such case, a second, cooperative terminalhaving a strong signal path between the base station is used to relaysignals between the first terminal and the base station. As a practicalmatter, this is likely to occur where the first terminal is subject tosevere channel fading while a second terminal is not, or where is aclear line of sight between the second terminal and base station, butnot between the first terminal and the base station.

For illustrative purposes, the architecture shown in FIG. 17 a includetwo base stations 1702 and 1704 and terminals 1706, 1708, and 1710. Inthe illustrated embodiment of FIG. 17 a, terminal 1706 has an antennaarray including Nt₁ transmit antennas, terminals 1708 has an antennaarray including Nt₂ transmit antennas, and terminal 1710 has an arrayincluding Nt₃ transmit antennas. Base station 1702 includes Nr₁ receiveantennas and base station 1704 includes Nr₂ receive antennas. In view ofthe foregoing MIMO definitions, the cooperative use of the terminalantennas increases the MIMO dimension to (Nt₁+Nt₂+Nt₃)*(Nr₁+Nr₂). Thisincrease in dimension is accomplished without requiring any additionalantenna elements at the terminals, as well as the components use todrive the antennas.

According to aspects of various embodiments of the invention describedherein, an information bit sequence corresponding to data to betransmitted to a base station may be space-time, space-frequency, orspace-time-frequency coded, as depicted by a block 1718 in FIG. 17 a.Space-time, space-frequency, or space-time-frequency codes may beaugmented to support delay diversity. After appropriate encoding isperformed in block 1718, the coded data is then passed to the terminals,whereupon it is transmitted via applicable antenna elements at thoseterminals. The terminals then perform joint MIMO transmissions (depictedas signals 1720, 1722, and 1724) towards the base stations in view ofapplicable MIMO channel configuration parameters. For example, signals1720, 1722, and 1724 transmitted from terminals 1706, 1708, and 1710 mayemploy selected antenna elements for each of the base stations based onthe coding scheme and/or MIMO scheme that is currently employed for aparticular base station. In general, cooperative MIMO transmissions canbe performed during regular communication, or during handoff, where aterminal moves across the boundary between cells.

In one embodiment, space-time coding is employed. For example, incominginformation bits are space-time coded (using e.g., space-time block ortrellis codes) at block 1718, and the encoded data are forwarded to eachof terminals 1706, 1708, and 1710. Further details of space-time blockencoding and the use of space-time trellis codes are discussed below.

In one embodiment, the space-time (or space-frequency, orspace-time-frequency) coding is performed at a master encoder. Inanother embodiment, the space-time (or space-frequency, orspace-time-frequency) is performed at separate locations (e.g., separatefrom each terminal, but typically co-located at a particular terminal)based on a common (replicated) information bit sequence received at eachof the separate locations.

It should be further appreciated that augmented antenna arrays can beused in uplink communications by employing the beamforming techniquesdescribed above with respect to downlink communications. Likewise, thetechniques known for steering transmitted signals toward selectedlocations, while transmitted signals sent toward other directions arenullified due to signal canceling effects and/or fading effects may befully employed for transmission from terminals to base stations. Similarto the discussion above, it may be necessary to employ signalsynchronization between multiple terminals to obtain the desiredbeamforming results.

FIG. 18 depicts cooperative MIMO architecture 1800 for uplinktransmissions. Information from multiple terminals is jointly encoded,transmitted from multiple terminals via the augmented MIMO antennaarray, and then decoded at the receiving base stations. In oneembodiment of the invention, the information is decoded at the basestations independently. The signals received at a base station butintended for another base station is treated as interference. In anotherembodiment, the information from all terminals is decoded jointly at thebase stations. In yet another embodiment, the information received atdifferent base stations is consolidated for joint decoding.

The embodiment of FIG. 18 shows an example of joint decoding. In thisinstance, information to be sent to multiple base stations, e.g., basestation 1806 and 1828, is jointly encoded using one of space-time,space-frequency, or space-time-frequency coding in a block 1830. Forclarity, the respective information to be sent to base station 1806 and1828 is depicted as data A and data B. The jointly encoded output ofblock 1830 is provided as inputs to each of base stations 1806 and 1828.The terminals then transmit the jointly encoded data via selectedantennas (corresponding to MIMO channels assigned to respective basestations) to base stations 1806 and 1828. Upon receipt of the jointlyencoded data, it is decoded via operations performed in a block 1832 foreach of base stations 1806 and 1828. Upon being decoded, informationintended for each recipient base station is kept, while otherinformation is discarded. Accordingly, base station 1806 keeps data Aand discards data B, while base station 1828 keeps data B and discardsdata A. In one embodiment, information to keep and discard is identifiedby packet headers corresponding to packets that are extracted from thedecoded data received at a given base station.

A block diagram corresponding to one embodiment of an OFDMA (OrthogonalFrequency Division Multiple Access) encoding/transmitter module 1900Afor a terminal having Nt transmit antennas is shown in FIG. 19 a.Information bits for each of 1-N subcarriers are received at respectivespace-time coding (STC) blocks 1904 _(1-N). The size of the STCs is afunction of the number of transmit antennas Nt. In general, thespace-time codes may comprise space-time trellis codes (STTC),space-time block codes (STBC), as well as STTC or STBC with delaydiversity, details of which are described below. Based on the applicableSTC, each of blocks 1904 _(1-p) outputs a set of code words to c₁[j,k]to c_(Nt)[j,k], wherein j represents the sub-channel index and k is thetime index. Each of the code words is then forwarded to an appropriateFast Fourier Transform (FFT) blocks 1906 _(1-Nt). The outputs of the FFTblocks 1906 _(1-Nt) are then fed to parallel to serial (PIS) conversionblocks 1910 _(1-Nt), and cyclic prefixes are added via add cyclic prefix(CP) blocks 1910 _(1-Nt). The outputs of add CP blocks 1910 _(1-Nt) arethen provided to transmit antennas 1-Nt to be transmitted as uplinksignals to various base stations for which the terminal iscommunicating.

A block diagram corresponding to one embodiment of an OFDMAreceiver/decoder module 2000 for a base station having Nr receiveantennas is shown in FIG. 20. The signal processing at the receive endof an uplink signal is substantially the inverse of the process used forencoding and preparing the signal for transmission. First, the cyclicprefix for each of the signals received at respective receive antennas1-Nr is removed by a respective remove CP block blocks 2010 _(1-Nr). Therespective signals are then fed into respective serial-to-parallel (SIP)conversion blocks 2008 _(1-Nt) to produce parallel sets of data, whichare then provided as inputs to FFT blocks 2006 _(1-Nr). The outputs ofFFT blocks 2006 _(1-Nr) are then forwarded to appropriate STC decodingblocks 2004 _(1-N) for decoding. The decoded data is then output at theinformation bits for subcarriers 1-N.

A block diagram corresponding to one embodiment of an OFDMAencoding/beamforming/transmitter module 1900B that performs uplinkbeamforming is shown in FIG. 19 b. As depicted by like-numbered blocks,much of the signal processing performed by the embodiments of FIGS. 19 aand 19 b is similar. In addition to these processing operations, OFDMAencoding/beamforming/transmitter module 1900B further includesbeamforming blocks 1905 _(1-N). Each of these beam forming blocksapplies a weighted value W_(1-N) to its respective inputs in view ofcontrol information provided by a beamforming control block 1912, whichis generated in response to beamforming feedback data 1914. Furtherdifferences between the embodiments of FIGS. 19 a and 19 b include STCblocks 1904A_(1-N) which now employ STCs having a size L, whichrepresents the number of beamforming channels.

Space Time Encoding.

Space-Time Codes (STC) were first introduced by Tarokh et at. from AT&Tresearch labs (Y. Tarokh, N. Seshadri, and A. R. Calderbank, “Space-timecodes for high data rates wireless communications: Performance criterionand code construction,” IEEE Trans. Inform. Theory, vol. 44, pp.744-765, 1998) in 1998 as a novel means of providing transmit diversityfor the multiple-antenna fading channel. There are two main types ofSTCs, namely space-time block codes (STBC) and space-time trellis codes(STTC). Space-time block codes operate on a block of input symbols,producing a matrix output whose columns represent time and rowsrepresent antennas. Space-time block codes do not generally providecoding gain, unless concatenated with an outer code. Their main featureis the provision of full diversity with a very simple decoding scheme.On the other hand, space-time trellis codes operate on one input symbolat a time, producing a sequence of vector symbols whose lengthrepresents antennas. Like traditional TCM (trellis coded modulation) fora single-antenna channel, space-time trellis codes provide coding gain.Since they also provide full diversity gain, their key advantage overspace-time block codes is the provision of coding gain. Theirdisadvantage is that they are difficult to design and generally requirehigh complexity encoders and decoders.

FIG. 9 shows a block diagram of as STC MIMO transmission model. Underthe model, data from an information source 900 is encoded using a STBCor SITC code by a space-time encoder 902. The encoded data is thentransmitted over a MIMO link 904 to a receiver 906. The received signalsare then decoded at the receiver to extract the original data.

An exemplary 8-PSK 8-state space-time trellis code for two antennas isshown in FIG. 10, while an exemplary 16-QAM 16-state SITC for twoantennas is shown in FIG. 11. The encoding for SITCs are similar to TCM,except that at the beginning and the end of each frame, the encoder isrequired to be in the zero state. At each time t, depending on the stateof the encoder and the input bits, a transition branch is selected. Ifthe label of the transition branch is c_(i) ^(t); c₂ ^(t); . . . ; c_(n)^(t), then transmit antenna i is used to send the constellation symbolsc_(i) ^(t)=1; 2; . . . ; n and all these transmissions are in parallel.In general, an SITC encoder may be implemented via a state machineprogrammed with states corresponding to the trellis code that is to beimplemented.

FIG. 12 shows a block diagram corresponding to an STBC model employingtwo antennas. As before, data is received from an information source1200. Space time block encoding is then performed by the operations ofspace time block code 1202 and constellation maps 1204A and 1204B.

In further detail, an STBC is defined by a pxn transmission matrix G,whose entries are linear combinations of x_(j); . . . ; x_(k) and theirconjugates x₁*; . . . ; x_(k)*, and whose columns arepairwise-orthogonal. In the case when p=n and {x_(i)} are real, G is alinear processing orthogonal design which satisfies the condition thatG^(T)G=D where D is a diagonal matrix with the (i;i) th diagonal elementof the form (l₁ ^(i)x+l₂ ^(i)x₂ ²+ . . . +l_(n) ^(i)x_(n) ²) with thecoefficients l₁ ^(i), l₂ ^(i), . . . l_(n) ^(i)>0. An example of a 2×2STBC code is shown in FIG. 12.

Another signal diversity scheme is to employ a combination of STC withdelay. For example, FIGS. 13 a and 13 b respectively show modelscorresponding to an STTC with delay transmission scheme and an STBC withdelay transmission scheme. In FIG. 13 a, data from an information source1300 is received by a code repetition block 1302, which produces a pairof replicated symbol sequences that are generated in view of the data. Afirst sequence of symbols is forwarded to an STTC encoder 1304A forencoding. Meanwhile, the replicated sequence of symbols is fed into adelay block 1306, which produces a one-symbol delay. The delayed symbolsequence output of delay block 1306 is then forwarded to STTC encoder1304B for encoding. An exemplary 8-PSK 8-state delay diversity code fortwo antennas is shown in FIG. 14. As illustrated, the symbol sequencefor transmission antenna Tx2 is synchronized with the input sequence,while the symbol sequence for transmission antenna Tx1 is delayed by onesymbol.

Under the signal diversity scheme of FIG. 13 b, data from informationsource 1300 is received at best block code selection logic 1308, whichoutputs replicated block codes to produce two block code sequences. Thefirst block code sequence is forwarded to constellation mapper 1310A forencoding, while the second block code sequence is delayed by one symbolvia a delay block 1312 and then forwarded to constellation mapper 1310Bfor encoding. The encoded signals are then transmitted via first andsecond transmit antennas.

The foregoing STTC and STBC schemes are depicted herein in accordancewith conventional usage for clarity. Under such usage, the variousencoded signals are transmitted using multiple antennas at the sametransmitter, e.g., a single base station. In contrast, embodiments ofthe invention employ selective antenna elements in antenna arrays frommultiple transmitters, e.g., multiple base stations and/or multipleterminals to form an augmented MIMO antenna array.

In order to implement an STC transmission scheme using multipletransmitters, additional control elements may be needed. For example, ifthe transmitters are located at different distances from a masterencoder facility, there may need to be some measure to synchronize theantenna outputs in order to obtain appropriate MIMO transmissionsignals. Likewise, appropriate timing must be maintained whenimplementing a delay diversity scheme using antenna arrays attransmitters at different locations.

FIG. 15 shows an example cooperative MIMO architecture 1500 that employsa master encoder 1502 serving base stations 402 and 404. However, itshould be appreciated that a master encoder could also serve multipleterminals, e.g., 1706, 1708, etc. In general, the master encoder 1502may be located at a separate facility from base stations or terminals,or may be co-located with one of the base stations or terminals. Inrespective embodiments, master encoder 1502 performs STC encoding andsignal processing operations similar to the operations performed by theOFDMA encoding/transmitter module 700A of FIG. 7A (as depicted in FIG.15) or OFDMA encoding/beamforming/transmitter module 700B of FIG. 7B.However, the transmission output are not fed directly to thetransmission antennas, since the transmission antennas for at least oneof the base stations or terminals will be located at a separatefacility. Rather, master encoder 1502 produces respective sets ofantenna drive signals 1504 and 1506 for base stations 402 and 404. Uponreceipt of the antenna drive signals, corresponding downlink signals aretransmitted by selected antennas hosted by base stations 402 and 404based on the different MIMO channels supported by the system. Controlinputs to master encoder 1502 corresponding to the MIMO channels areprovided by a subscriber MIMO channel assignment register 1508.

If necessary, signal synchronization is performed by one or moresync/delay blocks 1510. According to the example embodiment of FIG. 15,two sync/delay blocks 1510A and 1510B are shown, with each beingemployed at a respective base station. In other embodiments, some basestations or terminals may not require a delay block, particularly if aco-located master encoder is employed. In general, the sync/delay blocksfor a system are employed to synchronize the antenna signals orsynchronize the delay of antenna signals (when delay diversity isemployed).

Signal synchronization may be performed in any number of ways usingprinciples known in the communication arts. For example, in oneembodiment separate timing signals or sequences are provided to each ofthe base stations in a cooperative MIMO system. The timing signals orsequences contain information from which corresponding antenna drivesignals may be synchronized. To perform such synchronization, eachsync/delay blocks add an appropriate delay to its antenna signals.Synchronization feedback information may also be employed usingwell-known techniques.

Under one embodiment of a variation of architecture 1500, antenna signalprocessing operations corresponding to the FFT, PIS, and add CP blocksare implemented at the respective base stations or respective terminals.In this instance, STC code sequences are provided to each of the basestations or terminals, with further antenna signal processing beingperformed at the base stations or terminals. Under this approach, timingsignals or the like may be embedded in the data streams containing thecode sequences.

Another approach for implementing a cooperative MIMO system is depictedby cooperative MIMO architecture 1600 in FIG. 16. Under thisarchitecture, replicated instances of input information streams formultiple channel subscribers are generated by a block 1602 and providedto each of the base stations used to form the augmented MIMO antennaarray. In this case, the STC encoding and signal processing operationsare performed at each base station in a manner similar to that describedwith respect to the OFDMA encoding/transmitter module 700A of FIG. 7A(as depicted in FIG. 16) or OFDMA encoding/beamforming/transmittermodule 700B of FIG. 7B. Again, however, it should be appreciated thatarchitecture 1600 can also be implemented at the terminal side of anetwork, where input information streams generated by a block 1602 wouldbe provided to each terminal and used to form an augmented MIMO antennaarray.

In one embodiment, subscriber MIMO channel information is embedded inthe input data streams received at each base station. Accordingly, thereis a need to determine which antenna elements are used to support eachMIMO channel. This information is stored in a subscriber MIMO channelregister 1604, and is used to control signal processing in acollaborative manner at the base stations.

As before, there may be a need to synchronize the antenna signals. Forexample, if the components used to perform the operations of block 1602are located at different distances from the base stations, the inputstreams will be received at different times. In response, thecorresponding antenna signals will be generated at different times. Toaddress this situation, one or more sync/delay blocks 1606 may beemployed (e.g., as depicted by sync/delay blocks 1606A and 1606B in FIG.16B. In one embodiment, timing signals are encoded in the input datastreams using one of many well-known schemes. The timing signals, whichmay typically comprise timing frames, timing bits, and/or timingsequences, are extracted by 1606A and 1606B. In view of the timinginformation, a variable delay is applied by sync/delay block for thedata streams that are received earlier, such that at the point the datastreams are ready received at the STC blocks, they have beenresynchronized.

In general, the processing operations performed by the process blocksdepicted herein may be performed using known hardware and/or softwaretechniques. For example, the processing for a given block may beperformed by processing logic that may comprise hardware (circuitry,dedicated logic, etc.), software (such as is run on a general purposecomputer system or a dedicated machine), or a combination of both.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods, and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. A method comprising: employing antenna elementsfrom a plurality of base stations to support joint cooperativemultiple-input multiple-output (MIMO) transmissions in a wirelessnetwork, wherein the joint cooperative MIMO transmissions are orthogonalfrequency division multiple access (OFDMA) MIMO transmissions;replicating a data stream received from an information source;forwarding the replication of the data stream to each base station ofthe plurality of base stations; performing antenna signal processingoperations at each base station of the plurality of base stations on thereplication of the data stream it receives to generate antenna signals;transmitting the antenna signals over selected antenna elements of theantenna elements at each base station of the plurality of base stationsto form the joint cooperative MIMO transmissions; and encoding, atrespective base stations of the plurality of base stations, thereplication of the data stream using one of space-time coding,space-frequency coding, space-time-frequency coding, and spatialmultiplexing to establish the joint cooperative MIMO transmissions. 2.The method of claim 1, wherein the encoded joint cooperative MIMOtransmissions include subscriber MIMO channel information.
 3. The methodof claim 1, wherein the space-time coding comprises space-time trelliscoding.
 4. The method of claim 1, wherein the space-time codingcomprises space-time block coding.
 5. The method of claim 1, furthercomprising: encoding the joint cooperative MIMO transmissions usingspace-time coding with delay diversity.
 6. The method of claim 1,wherein the joint cooperative MIMO transmissions include downlinktransmission s from the plurality of base stations to terminals anduplink transmissions from the terminals to the plurality of basestations.
 7. The method of claim 1, further comprising: performingspatial beamforming for selected ones of the joint cooperative MIMOtransmissions.
 8. The method of claim 7, wherein the spatial beamformingis performed in combination with one of space-time, space-frequency andspace-time-frequency coding of the selected ones of the jointcooperative MIMO transmissions.
 9. The method of claim 1, furthercomprising: transmitting the joint cooperative MIMO transmissions to atleast two terminals simultaneously.
 10. The method of claim 9, furthercomprising: performing spatial beamforming on the joint cooperative MIMOtransmissions such that MIMO transmissions are directed toward intendedusers while spatial nulling is effected toward unintended users.
 11. Themethod of claim 1, further comprising: decoding, jointly, uplink MIMOtransmissions received from multiple terminals.
 12. The method of claim1, further comprising: decoding, jointly, downlink MIMO transmissionsreceived at multiple terminals.
 13. The method of claim 1, furthercomprising: decoding, separately, uplink MIMO transmissions receivedfrom multiple terminals.
 14. The method of claim 1, further comprising:encoding, jointly, downlink MIMO transmissions sent to multipleterminals.
 15. The method of claim 14, further comprising: decoding ajointly encoded downlink MIMO transmission at a terminal of the multipleterminals; and keeping portions of data sent via the jointly encodeddownlink MIMO transmission intended for the terminal, while discardingother portions of the data that are not intended for the terminal. 16.The method of claim 14, further comprising: separately decoding,separately, the jointly encoded downlink transmissions at each of themultiple terminals.
 17. The method of claim 1, further comprising:synchronizing performance of the antenna signal processing operations atthe plurality of base stations such that the antenna signals aretransmitted over the selected antenna elements at different basestations of the plurality of base stations in synchrony.
 18. The methodof claim 1, further comprising: performing the joint cooperative MIMOtransmissions to facilitate terminal handoff between wireless networkcells or sectors.
 19. The method of claim 1, further comprising:performing MIMO encoding on another data stream to be transmitted over acorresponding joint cooperative MIMO channel, the MIMO encodingproducing a respective set of encoded data sequences for each basestation of the plurality of base stations; sending to each base stationof the plurality of base stations the respective set of encoded datasequences produced therefor; performing other antenna signal processingoperations to generate other antenna signals at each base station of theplurality of base stations in view of the respective sets of encodeddata sequences received thereby; and transmitting the other antennasignals over corresponding antenna elements of the antenna elements ateach base station of the plurality of base stations to transmit theanother data stream over the corresponding joint cooperative MIMOchannel.
 20. The method of claim 19, further comprising: synchronizingthe performance of the other antenna signal processing operations at theplurality of base stations such that the other antenna signals aretransmitted over the selected antenna elements at different basestations of the plurality of base stations in synchrony.
 21. A multicellwireless network, comprising: a plurality of base stations eachassociated with a respective cell and having a respective antenna arrayincluding at least one antenna element; a joint cooperativemultiple-input multiple-output (MIMO) transmission mechanism thatemploys selected antenna elements from the plurality of base stationsto: form an augmented antenna array used to support joint cooperativeMIMO transmissions over the wireless network, wherein the jointcooperative MIMO transmissions are orthogonal frequency divisionmultiple access (OFDMA) MIMO transmissions; and encode, at respectivebase stations of the plurality of base stations, the replication of thedata stream using one of space-time coding, space-frequency coding,space-time-frequency coding, and spatial multiplexing to establish thejoint cooperative MIMO transmissions; a data replicator to: replicate adata stream received from an information source; and forward thereplication of the data stream to each base station of the plurality ofbase stations; and a set of antenna signal processing components at eachbase station of the plurality of base stations to perform antenna signalprocessing operations on the data stream it receives to generate antennasignals, wherein the antenna signals are transmitted over the selectedantenna elements to form a joint cooperative MIMO transmission at eachbase station of the plurality of base stations.
 22. The multicellwireless network of claim 21, wherein the encoded joint cooperative MIMOtransmissions include subscriber MIMO channel information.
 23. Themulticell wireless network of claim 21, wherein the space-time codingcomprises space-time trellis coding.
 24. The multicell wireless networkof claim 21, wherein the space-time coding comprises space-time blockcoding.
 25. The multicell wireless network of claim 21, wherein thejoint cooperative MIMO transmission mechanism encodes the jointcooperative MIMO transmissions using space-time coding with delaydiversity.
 26. The multicell wireless network of claim 21, wherein thejoint cooperative MIMO transmissions include downlink transmissions fromthe plurality of base stations to terminals and uplink transmissionsfrom the terminals to the plurality of base stations.
 27. The multicellwireless network of claim 21, wherein the joint cooperative MIMOtransmission mechanism performs spatial beam forming for selected onesof the joint cooperative MIMO transmissions.
 28. The multicell wirelessnetwork of claim 27, wherein the joint cooperative MIMO transmissionmechanism performs the spatial beamforming in combination with one ofspace-time, space-frequency and space-time-frequency coding of theselected ones of the joint cooperative MIMO transmissions.
 29. Themulticell wireless network of claim 21, wherein the joint cooperativeMIMO transmission mechanism performs transmitting the joint cooperativeMIMO transmissions to at least two terminals simultaneously.
 30. Themulticell wireless network of claim 29, wherein the joint cooperativeMIMO transmission mechanism further perforins spatial beamforming on thejoint cooperative MIMO transmissions such that MIMO transmissions aredirected toward intended users while spatial nulling is effected towardunintended users.
 31. The multicell wireless network of claim 21,wherein the joint cooperative MIMO transmission mechanism furtherperforms jointly decoding uplink MIMO transmissions received frommultiple terminals.
 32. The multicell wireless network of claim 21,wherein the joint cooperative MIMO transmission mechanism furtherperforms separately decoding uplink MIMO transmissions received frommultiple terminals.
 33. The multicell wireless network of claim 21,wherein the joint cooperative MIMO transmission mechanism furtherperforms jointly encoding downlink MIMO transmissions sent to multipleterminals.
 34. The multicell wireless network of claim 21, furthercomprising: a synchronizing mechanism to synchronize the antenna signalprocessing operation s at the plurality of base stations such that theantenna signals are transmitted over the selected antenna elements atdifferent base stations of the plurality of base stations in synchrony.35. The multicell wireless network of claim 21, further comprising: amaster encoder to: perform MIMO encoding on another data stream to betransmitted over a corresponding joint cooperative MIMO channel, theMIMO encoding producing a respective set of encoded data sequences foreach base station of the plurality of base stations; and send to eachbase station of the plurality of base stations the respective set ofencoded data sequences produced therefor; and a set of other antennasignal processing components at each base station of the plurality ofbase stations to perform other antenna signal processing operations onthe respective sets of encoded data sequences received thereby togenerate other antenna signals, wherein the other antenna signals aretransmitted over the selected antenna elements at each base station ofthe plurality of base stations to form the joint cooperative MIMOtransmissions over the corresponding joint cooperative MIMO channel. 36.The multicell wireless network of claim 35, further comprising: asynchronizing mechanism to synchronize the other antenna signalprocessing operations at the plurality of base stations such that theother antenna signals are transmitted over the selected antenna elementsat different base stations of the plurality of base stations insynchrony.
 37. The multicell wireless network of claim 21, wherein thejoint cooperative MIMO transmission mechanism performs the jointcooperative MIMO transmissions to facilitate terminal handoff betweenwireless network cells or sectors.